The metal rod ones that fold up into a bundle have lots of weak points. If you look at hunting stools/chairs which are made out of 1.5" aluminum tube, they are a hell of a lot stronger. The problem is they fold flat, but not into a bundle. I've seen 500 lb guys use them. Check out B*** Pro or Cabellas. They are also lighter I think then the rod ones.
I'm 6-3 and pushing 300 lbs and never felt unsteady in one. If anyone needs a link, let me know.
Yes, please post a link to any foldable chair that can hold over 400 lbs. I would love to have something to leave in the car for emergencies. TIA
Try a catalog/website called Living XL. They have everything from chairs to scales. I think they even have some clothes too.